1. Prior Art
The prior art appears to be best exemplified by the following patents which were developed in a search:
______________________________________ Banczak 4,021,252 5/77 Wachtel 4,024,096 5/77 Parkinson 4,045,397 8/77 Hwang 4,070,322 1/78 Hainsworth 2,798,855 7/57 Hainsworth 2,798,856 7/57 Crone 3,078,182 2/63 Carumpalos 3,288,718 11/66 Edenbaum 3,311,084 3/67 Edenbaum 3,360,337 12/67 Edenbaum 3,360,339 12/67 Edenbaum 3,360,338 12/67 Bhiwandker 3,523,011 8/70 Verses 3,704,096 11/72 Edenbaum 3,386,807 6/68 Chapman 3,862,824 1/75 ______________________________________
2. Field of the Invention
This invention relates to adhesive tapes bearing on their surfaces ink compositions and particularly jet ink compositions that are particularly useful as sterilization and/or moist thermal exposure indicators.
Indicator tapes of various types are known in the art. For the most part, such materials employ inorganic pigment combinations or must employ a heat-curable agent in the adhesive layer to provide a tape of satisfactory adhesive characteristics during exposure to the elevated temperatures involved in the sterilization techniques. With many of the prior art tapes, manufacture of the tape itself is not without problems since it may be necessary to cure the adhesive during the manufacture of the tape to obtain satisfactoy adhesion properties and it is often difficult to avoid premature color change of the colorants during the heat curing of the heat activatable adhesive. Still other problems are related to the colorants employed, many of which are either too sensitive and activate at too low a temperature or are too insensitive and activate at too high a temperature. Some react to dry heat regardless of the presence of essential moisture thus giving a misleading sterilization indication. Some are unduly photosensitive and deteriorate excessively in the presence of light. Some give only transient or reversible indications or are dependent on the particular substrate on which they are printed and still others are relatively expensive, are not readily printable or impart, prior to sterilization, undesired color to the substrate.
It is an object of this invention to provide indicator tapes which show a distinct difference in color among sterilized and unsterilized packages.
It is another object of this invention to provide a positive and visible indication that packages have been subjected to temperatures at which sterilization or pasteurization of the products contained therein may be achieved.
It is another object of this invention to provide indicator tapes which may comprise a variety of plastic carriers having on their surfaces an ink composition, applied thereto by either conventional coating or by jet printing techniques.
These and other objects of the invention will be apparent from the description of the invention which follows.